225
FXCA62 TJSJ 030755
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
355 AM AST Thu Jul 3 2025

.KEY MESSAGES...

 * Saharan dust will persist across the region through at least
   Sunday.

 * A Heat Advisory is in effect today from 10 AM to 4 PM for most
   coastal areas of Puerto Rico. Heat index values between 108F
   and 111 F are expected. Residents should stay hydrated and
   take frequent breaks when working outdoors.

 * A moderate risk of rip currents is present along the northern
   and eastern coasts of Puerto Rico and the U.S. Virgin Islands.

&&

.SHORT TERM...Today through Saturday...

Mostly tranquil conditions were observed across the islands through
the night hours. Some showers managed to move into eastern Puerto
Rico and the Virgin Islands, but rainfall accumulations were
minimal. Temperatures cooled down to the low and mid 60s in the
mountain, and into the 70s in coastal areas. The most recent
satellite derived precipitable water imagery shows an area of less
moisture approaching the Virgin Islands, so showers will gradually
taper off later this morning.

The winds will be driven by a surface high pressure over the central
Atlantic, coming out of the southeast at 10 to 15 kts, with stronger
gusts. These winds will make temperatures soar into the upper 80s
and low 90s, and with heat indices exceeding 108 degrees in some
urban and coastal areas, especially along northern and western
Puerto Rico. This level of heat affects most individual sensitive to
heat, especially those without effective cooling or adequate
hydration. Even if moisture is nearly average today, strong heating
should trigger showers and thunderstorms across the interior and
northwestern Puerto Rico, where isolated urban flood cannot be ruled
out.

Tomorrow, a weak tropical wave will approach the region. The
increase in moisture will once again trigger afternoon convection,
for the interior, west, and around the San Juan metropolitan area.
Other sections of the Virgin Islands, eastern and southern Puerto
Rico will receive some showers as well. After the wave departs,
Saharan dust will arrive, in moderate to high concentrations. This
will result in hazy skies, reduced visibilities and a deterioration
in air quality. Some low level moisture will be embedded in the
dust, so it will not be completely dry. Temperatures will continue
to be above normal in the next couple of days, so heat advisories
are likely each day.

.LONG TERM...Sunday through Thursday....

A relatively variable weather pattern is forecast across the
region from Sunday through Thursday, influenced by several upper-
level features, surface patterns, and an intrusion of Saharan dust
by the beginning of the period. On Sunday, there will be a slight
presence of instability aloft due to a cut-off low located over
Hispaniola that might result in moisture advection across the
area. Meanwhile, at the mid-levels (500700 MB), a ridge will help
maintain a relatively stable environment aloft. At the same time,
a plume of Saharan dust is expected to move over the region, with
concentrations capable of reducing visibility between 0.20 and
0.30 inches, resulting in hazy skies and possible air quality
deterioration. Overall, Sunday appears to be a quiet day with hazy
skies and limited shower development. However, daytime heating
and the local mountains will lead to the development of afternoon
convection, particularly in the interior and western parts of
Puerto Rico. Similar activity will be possible for the U.S. Virgin
Islands in isolated areas, mostly in the evening hours.

By Monday, another cut-off low will migrate from the northeast
into the northern portion of the region, further increasing
moisture levels and cloudiness. This upper-level feature will
enhance patches of cloudiness and moisture, which will be
transported westward by the prevailing easterly trade winds. The
interaction between this feature, surface heating, and local
effects will result in scattered showers and isolated afternoon
thunderstorms, mainly over the interior and western sections of
Puerto Rico each day. Trade winds will persist from the east under
the influence of a broad surface high pressure system stall over
the central Atlantic. On Thursday, the pattern will remain
similar, with southeast winds gradually taking hold as a broad
surface high over the central Atlantic extends further into the
Caribbean. Days will remain variable, with occasional passing
showers in the trade wind flow during the morning and overnight
hours, followed by pockets of afternoon convection over interior
and western Puerto Rico. So far today, although model had some
high level of uncertainty, Wednesday into Thursday will be the
most unstable days for the long term period.

&&

.AVIATION...
(06Z TAFS)

Mostly VFR conditions expected to prevail through the forecast
period. Passing SHRA are expected across the Caribbean and Atlantic
waters, but with little impacts to operations. After 17Z, TSRA is
expected near TJBQ, with periods of reduced VIS and low ceilings.
Winds will be from the ESE at 8-17 kts, with stronger gusts.

&&

.MARINE...
A broad surface high pressure over the central Atlantic will
continue to result in moderate to fresh easterly winds across the
region. Therefore, wind-driven seas will result in choppy marine
conditions across the Atlantic waters and the Caribbean Waters.
Saharan dust particles will be in place, resulting in hazy skies
and limited shower activity until Friday, when another tropical
wave moves into the islands, bringing showers and thunderstorms.

&&

.BEACH FORECAST...
The wind-driven seas will continue to result in choppy marine
conditions across the coastal local waters. Therefore, there will
be a moderate risk of rip currents across northern and
northeastern PR. The risk will return to low by Friday.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for PRZ001>005-007-008-010-011.

VI...None.
AM...None.
&&

$$

SHORT TERM...ERG
LONG TERM....LIS
AVIATION...ERG